CAT37
CMOS White LED Driver
Boost Converter
Description
The CAT37 is a DC/DC step up converter that delivers a regulated
output current. Operation at a constant switching frequency of
1.2 MHz allows the device to be used with very small value external
inductor and ceramic capacitors.
The CAT37 is targeted to drive multiple white light−emitting diodes
(LEDs) connected in series and provides the necessary regulated current
to control the brightness and the color purity. An external resistor R1
controls the output current level. LED currents of up to 40 mA can be
supported over a wide range of input supply voltages from 2.5 V to 7 V,
making the device ideal for battery−powered applications.
A high voltage output stage allows up to 4 White LEDs to be driven
in series. Series drive provides inherent current matching.
LED dimming can be done by using a DC voltage, a logic signal, or
a pulse width modulation (PWM) signal. The shutdown input pin
allows the device to be placed in power−down mode with “near zero”
quiescent current.
In addition to overcurrent limiting protection, the device also
includes detection circuitry to ensure protection against open−circuit
load fault conditions.
The device is available in a low profile (1 mm max height) 5−lead
TSOT−23 package.
Features
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TSOT−23
TD SUFFIX
CASE 419AE
PIN CONNECTIONS
1
SW
GND
FB
(Top View)
1 mm Maximum Height
q
JA
= 250°C/W (free air)
SHDN
VIN
MARKING DIAGRAM
•
•
•
•
•
•
•
•
•
•
•
•
•
Low Quiescent Ground Current (0.5 mA Typical)
Power Efficiency Over 80%
Compatible Pinout with LT1937
Adjustable Output Current (up to 40 mA)
High Frequency 1.2 MHz Operation
Input Voltage Operation down to 2.5 V
Low Resistance (0.5
W)
Power Switch
Drives up to 4 White LEDs in Series
Shutdown Current Less than 1
mA
Load Fault Protection Against Open−circuits
Low Value External Components
Low Profile (1 mm) TSOT−23 5−lead Package
These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
Compliant
Color LCD and Keypad Backlighting
Cellular Phones
Handheld Terminals
Digital Cameras
PDAs/Games
Portable MP3 Players
1
LMYM
ULYM
LM = CAT37TDI−T3
UL = CAT37TDI−GT3
Y = Production Year (Last Digit)
M = Production Month (1−9, A, B, C)
ORDERING INFORMATION
Device
CAT37TDI−T3
(Note 1)
CAT37TDI−GT3
(Note 2)
Package
TSOT−23
(Pb−Free)
TSOT−23
(Pb−Free)
Shipping
3,000/
Tape & Reel
3,000/
Tape & Reel
Applications
•
•
•
•
•
•
1. Matte−Tin Plated Finish (RoHS−compliant).
2. NiPdAu Plated Finish (RoHS−compliant).
©
Semiconductor Components Industries, LLC, 2010
February, 2010
−
Rev. 21
Publication Order Number:
CAT37/D
CAT37
Typical Application Circuit
VIN
3 V to 5 V
C1
1
mF
5
VIN
CAT37
ON OFF
4
SHDN
GND
2
FB
3
L1 6.8
mH
D1
1
SW
15 mA
R
1
6.34
W
C2
1
mF
C1: Taiyo Yuden JMK212BJ475
C2: Taiyo Yuden EMK212BJ105
L1: Panasonic ELJEA6R8 or equivalent
Figure 1. Driver for Four High−Brightness White LEDs
Table 1. PIN DESCRIPTION
Pin Number
1
2
3
4
5
Name
SW
GND
FB
SHDN
VIN
Function
Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area
connected to this pin.
Ground pin. Connect pin 2 to ground.
LED (cathode) connection pin.
Shutdown pin.
Input supply pin. This pin should be bypassed with a capacitor to ground. A 1
mF
capacitor mounted
close to the pin is recommended.
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
V
IN
, FB, SHDN voltage
SW voltage
Storage Temperature Range
Junction Temperature
Lead Soldering Temperature (10 secs)
ESD Rating – Human Body Model
Rating
8
20
−65
to +160
125
300
2000
Unit
V
V
°C
°C
°C
V
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
Table 3. RECOMMENDED OPERATING CONDITIONS
Parameter
V
IN
Ambient Temperature Range
Inductor L1
Input Capacitor C1
Output Capacitor C2
I
LED
with 1 to 4 LEDs in series
NOTE:
Typical application circuit with external components is shown above.
Range
2.5 to 7
−40
to +85
6.8
±
20% typical
1.0
±
20% typical
1.0
±
20% typical
0 to 20
Unit
V
°C
mH
mF
mF
mA
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CAT37
Table 4. ELECTRICAL OPERATING CHARACTERISTICS
(Over recommended operating conditions unless otherwise specified. T
A
= 25°C, V
IN
= 3 V and V
SHDN
= 3 V.)
Symbol
Parameter
Input Voltage Range
I
Q
I
SD
V
FB
I
FB
Quiescent Current
Shutdown Current
FB Pin Voltage
FB Pin Leakage Current
Shutdown High Threshold
Shutdown Low Threshold
I
SHDN
f
SW
DC
I
SWL
Shutdown Pin Current
Boost Converter Frequency
Maximum Switch Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Efficiency
I
SW
= 300 mA
Switch Off, V
SW
= 5 V
Figure 1 with specified components
0.8
90
400
1.2
95
550
150
0.01
83
780
200
5
0.85
0.25
1
1.6
V
FB
= 0.2 V
V
SHDN
= 0 V
4 LEDs at 15 mA
85
Conditions
Min
2.5
0.5
0.05
95
1
Typ
Max
7
0.7
1
105
2
Units
V
mA
mA
mV
mA
V
V
nA
MHz
%
mA
mV
mA
%
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CAT37
TYPICAL CHARACTERISTICS
(V
IN
= 3.6 V, T
AMB
= 25°C, C
IN
= 4.7
mF,
C
OUT
= 1
mF,
L = 6.8
mH,
unless otherwise specified.)
30
3 LEDs
LED CURRENT (mA)
LED CURRENT (mA)
20 mA
20
15.5
4 LEDs
15.0
16.0
10 mA
10
14.5
0
2
3
4
INPUT VOLTAGE (V)
5
6
14.0
−50
−25
0
25
50
75
100
TEMPERATURE (°C)
Figure 2. LED Current vs. Input Voltage
110
105
FB PIN VOLTAGE (mV)
FB PIN VOLTAGE (mV)
95
100
95
90
85
80
80
−50
100
Figure 3. LED Current vs. Temperature
3 LEDs
90
85
4 LEDs at 15 mA
VIN = 3.6 V
0
5
10
LED CURRENT (mA)
15
20
−25
0
25
50
75
100
TEMPERATURE (°C)
Figure 4. FB Pin Voltage vs. LED Current
1.3
1.2
1.1
1.0
0.9
4 LEDs
0.8
1
2
3
4
5
6
SWITCHING FREQUENCY (MHz)
SWITCH FREQUENCY (MHz)
1.3
1.2
1.1
Figure 5. FB Pin Voltage vs. Temperature
LOAD = 20 mA
1.0
0.9
0.8
−50
LOAD = 3 LEDs
VIN = 3.6 V
−25
0
25
50
75
100
INPUT VOLTAGE (V)
TEMPERATURE (°C)
Figure 6. Switching Frequency vs. Input
Voltage
Figure 7. Switching Frequency vs.
Temperature
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CAT37
TYPICAL CHARACTERISTICS
(V
IN
= 3.6 V, T
AMB
= 25°C, C
IN
= 4.7
mF,
C
OUT
= 1
mF,
L = 6.8
mH,
unless otherwise specified.)
90
85
80
75
70
65
60
3 LEDs at 15 mA
VOUT = 10 V
EFFICIENCY (%)
EFFICIENCY (%)
86
84
82
80
78
76
74
−50
LOAD = 3 LEDs
VIN = 3.6 V
−25
0
25
50
75
100
LOAD = 20 mA
LOAD = 15 mA
LOAD = 10 mA
2
3
4
INPUT VOLTAGE (V)
5
6
TEMPERATURE (°C)
Figure 8. Efficiency vs. Input Voltage
Figure 9. Efficiency vs. Temperature
Figure 10. V
SW
, I
L
, & V
OUT
Waveforms
Figure 11. PWM on SHDN Pin at 1 kHz
Figure 12. Enable Power−Up Waveforms
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